Flexible power cable

ABSTRACT

A flexible power cable for use on mining machines has a central insulated ground check strand comprising conductor wires that are wound around a stretchable tensile core.

United States Patent Hansen et al.

[451 Oct. 17, 1972 [54] FLEXIBLE POWER CABLE I72] Inventors: Theodore E.Hansen; Floyd A. W"-

son, both of Marion, Ind.

[73] Assignee: Annclndn Wire and Cable Company [22} Filed: Feb. 29, 1972[21] Appl. No.: 230,364

[52] U.S.Cl ..174/l15,l74/116 [51] Int. Cl. "HO lb 9/00 [58] FieldofSearch ..l74/ll5, 113 R, 113 C, 116, 174/27, 110 AR, 110 N, 13] A [56]References Cited UNITED STATES PATENTS Morrison ..l74/1 15 X 2,930,8373/1960 Thompson ..l74/1l5 3,644,659 2/1972 Campbell ..l 74/l l5 X3,621,118 ll/l97l Bunish ..l74/ll5 Primary Examiner-Lewis H. MyersAssistant Examiner-A. T. Grimley Attorney-Victor F. Volk [57] 7 ABSTRACTA flexible power cable for use on mining machines has a centralinsulated ground check strand Comprising conductor wires that are woundaround a stretchable tensile core.

6 Claims, 4 Drawing Figures BACKGROUND OF THE INVENTION Mining machinecables may be either flat, with the conductors laid parallel to eachother, or round, with the conductors wound in a helix, and the equipmentwith which the cables are used is usually designed to accommodate one orthe other cable shape. The present invention relates to round cables,rather than fiat. Mining machine cables in common use have comprisedthree helically-wound insulated power conductors, and three uninsulatedgrounding conductors cabled in the interstices formed by the insulatedconductors. More recently it has been required by government regulationsto include an insulated ground check strand for monitoring the integrityof the grounding conductors. This has been laid in one of theinterstices in substitution of one of the grounding conductors. Such'acable configuration has, it is now found, a serious disadvantage due toits assymetry, in that unbalanced electrical potentials are induced inthe grounding conductors.

SUMMARY By means of our present invention we propose to avoid structuraland electrical imbalance in a threephase cable having groundingconductors and a ground check strand, while providing that the groundcheck strand shouldwithstand elongation of the cable in use and outlastthe grounding conductors on repeated cable flexing.

Our flexible power cable comprises three insulated power currentconductors helically stranded together, three grounding conductors woundin the interstices of the power conductors, and a central insulatedgroundcheck strand. The ground check strand comprises a resilientlystretchable tensile member such, for preferred examples, as polyvinylchloride extrusions, and pluralities of nylon filaments. A plurality ofground-check wires are wound in a short lay-length around the tensilemember. A'second plurality of wires may advantageously be wound overthese in an opposite direction of lay. A cylindrical wall of polymericinsulation surrounds the wires of the ground-check strand and anabrasion-resistant polymeric jacket covers the cable overall,surrounding the conductors and the grounding strands. Preferably theinsulated conductors, and ground-check wires comprise copper.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE shows a pictorial view of acable made to our invention, with portions cut away to expose the insidecable elements.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT As illustrative of ourinvention, we have shown in the FIGURE a 3-conductor, Awg 4/0 cable, for600 volt service, made in accordance with our teachings and designatedgenerally by the numeral 10. The cable has three power currentconductors ll, 12, 13 each made up of 532 tinned copper wires andcovered with respective walls 14, l5, 16 of olefinic copolymerinsulation 0.080 inch thick. The conductors 11, l2, 13 are helicallycabled around a ground check strand l7, hereinafter to be more fullydescribed, and cabled in the interstices of the conductors 11, l2, 13are three Awg No. 3 grounding conductors l8, 19, 20 each stranded of 259tinned copper wires. Conventional neoprene cable fillers 21 fill hollowsremaining in the interstices and round out the core configuration aroundwhich is applied a conventional binder tape 22 which is surrounded witha first extruded neoprene jacket 23,

5/64 inch thick, an open weave nylon seine twine reinforcing web 24, andan overall neoprene jacket 26, 8/64 inch thick. The diameter over thejacket 26 is 2.04 inches. v

The ground check element 17 has a tensile core 27 made up of seven 0.025inch nylon monofilaments laid parallel and compressed to a 0.060 inchdiameter by a serving 28 of 20 ends of tinned copper wires of 0.008 inchdiameter wound with a left hand lay of )4 inch pitch and an overlyingserving 29 of 20 ends of 0.008 inch diameter tinned copper wires woundat a )4 inch pitch in a right hand lay. Variations of pitch may be usedwithin the scope of our invention, but the copper wires are required tohave a short lay such as a lay not substantially exceeding five timesthe diameter over the core. The ends may also vary and the minimum laylength will be determined by the number of ends that is chosen. It isnot essential, either, that the servings should have opposite directionsof lay and both might have either right hand or left hand lays withinour inventive concept. A polyester film separator 31, 0.0005 inch thick,is wrapped longitudinally over the wires 29 and an 0.030 inch wall 32 ofpolypropylene is extruded over the separator 31.

It is well known that when a cable is flexed, the central member of astranded cable undergoes greater elongation than the members that arewound helically over it. It is for this reason that the ground checkstrand, which is required to outlast the other cable members hasheretofore been wound into one of the outer cable interstices. It hasbeen found, however, that although the ground check strand 17 iscentered in the cable 10 it does outlast the grounding conductors l8,19, 20 in flexing tests and in field service.

To test the need and efficacy of the present improvement a foot lengthof a cable corresponding to the cable 10 was laid in a figure U with oneend connected to a three-phase motor alternator set having a relativelypure sinusoidal output and the other end connected to a balanced 1000watt per phase load. The grounding connectors wereconnected to eachother at both ends of the cable and grounded at the generator end.Induced voltage in the grounding conductors was measured at the load endand is reported in the TABLE below as specimen A for the conditioncorresponding to the present construction and as specimen B where one ofthe grounding conductors was opened to simulate the conditions of theabove-mentioned prior art cable having one of the grounding conductorsreplaced by the ground-check strand.

TABLE Measured potential, ground- Phase current ing conductors, volts Inthe illustrative cable we have employed seven nylon monofilaments forthe tensile core 27 of our ground-check strand 17. This number, and,indeed the use of nylon is not limiting, the important features beingthat the core should have enough tensile strength to pull the strand 17through the extruder during the extrusion of the wall 32, that it shouldstretch without breaking when the cable 10 is flexed, that it shouldrecover substantially to its original dimensions when the cable 10 isagain straightened and, very importantly, that the elongation of thecore 27 should be accompanied by a reduction of its diameter so that thepitch of the helix of the wires 28, 29 will be free to lengthen. Uponrelaxation it is again advantageous that the diameter of the core 27should increase to till the helix formed by the wires 28, 29.

We have found that the necessary requirements for a satisfactory corewill be met by a polyvinyl extrusion or, indeed, any polymeric materialhaving a tensile strength exceeding a few hundred pounds per squareinch, but preferably over 1000 pounds per square inch, and substantiallyfull recovery from an elongation of 5 percent or more. It is not met,however, by a mere paste or uncured wax or unvulcanized rubber.

We have invented a new and useful power cable of which the foregoingdescription has been exemplary rather than definitive and for which wedesire an award of Letters Patent as defined in the following claims.

We claim:

1. A flexible power cable comprising:

A. three insulated power current conductors helically stranded together,

B. three grounding conductors wound in the interstices of said powercurrent conductors,

C. a central insulated ground-check strand compris- 1. a resilientlystretchable tensile member,

2. a plurality of ground-check wires wound in a short lay-length aroundsaid member,

3. a cylindrical wall of polymeric insulation surrounding said wires,and

D. an abrasion-resistant polymeric jacket surrounding said insulatedconductors and said grounding conductors.

2. The cable of claim 1 wherein said power current conductors, saidgrounding conductors, and said ground-check wires comprise copper.

3. The cable of claim 1 wherein said ground-check strand comprises asecond plurality of ground-check wires wound around said member, saidpluralities of wires being wrapped one over the other.

4. The cable of claim 1 wherein said tensile member comprises apolyvinyl chloride extrusion.

5. The cable of claim 1 wherein said tensile member comprises nylon. v

6. The cable of claim 5 wherein said tensile member comprises aplurality of filaments.

1. A flexible power cable comprising: A. three insulated power currentconductors helically stranded together, B. three grounding conductorswound in the interstices of said power current conductors, C. a centralinsulated ground-check strand comprising,
 1. a resiliently stretchabletensile member,
 2. a plurality of ground-check wires wound in a shortlaylength around said member,
 3. a cylindrical wall of polymericinsulation surrounding said wires, and D. an abrasion-resistantpolymeric jacket surrounding said insulated conductors and saidgrounding conductors.
 2. a plurality of ground-check wires wound in ashort lay-length around said member,
 2. The cable of claim 1 whereinsaid power current conductors, said grounding conductors, and saidground-check wires comprise copper.
 3. The cable of claim 1 wherein saidground-check strand comprises a second plurality of ground-check wireswound around said member, said pluralities of wires being wrapped oneover the other.
 3. a cylindrical wall of polymeric insulationsurrounding said wires, and D. an abrasion-resistant polymeric jacketsurrounding said insulated conductors and said grounding conductors. 4.The cable of claim 1 wherein said tensile member comprises a polyvinylchloride extrusion.
 5. The cable of claim 1 wherein said tensile membercomprises nylon.
 6. The cable of claim 5 wherein said tensile membercomprises a plurality of filaments.